fayechristian Posted December 17, 2012 Report Share Posted December 17, 2012 Please help I have a white glaze that randomly turns yellow. I can use the same glaze for a whole kiln full of work and some pieces turn out snow white while their neighbour is totally toxic yellow. The recipe is: Potash Feldspar 33 Talc 21 Quartz 16 China Clay 15 Whiting 12 Zinc 3 + Titanium dixide 3 Tin Oxide On earthstone ES160 special clay I fire to cone 9 in an electric kiln with a ventsure extraction system. I bisc to cone 06 - if that information can be of any help? My own theories have been: Contamination from chrome fumes? but it still happens even when there's not chrome in the kiln. The other glazes I use are iron or copper based. Patches of reduction? but it happens to one pot and not it's neighbour some times and in relatively empty kilns some times too. It also happens in different areas of the kiln. I'm not ruling out thickness of application either but it's not the clay showing through it's a sort of bright toxic yellow fog in the glaze, it's also not as shiny as the white. Help/ideas/theories/general musings welcome Link to comment Share on other sites More sharing options...
TJR Posted December 17, 2012 Report Share Posted December 17, 2012 I am not a glaze doctor, so don't quote me, but I am wondering what the titanium is doing for your glaze. The tin is the opacifier, and is what is making a beautiful white matt. Try a 100 gram test,leaving out the titanium, make a couple bisque test tiles,glaze them, and spread them throughout the kiln and see if this helps. I am thinking that the titanium is the base for rutile. 3% rutile in a glaze will give you yellow. As I said, I am not an expert, but am pretty experienced with glazes. TJR Link to comment Share on other sites More sharing options...
Brian Reed Posted December 18, 2012 Report Share Posted December 18, 2012 Instread of tin you may try Zircopax plus. I use it at 10% in my plain 4321 white and it comes out great. Link to comment Share on other sites More sharing options...
fayechristian Posted December 18, 2012 Author Report Share Posted December 18, 2012 I love this forum! Thanks for the replys all of which are great ideas. I'd like to meet one of these 'glaze doctors' This is a picture of the piece which pushed me over the edge hopefully you can see the beautiful translucent white glaze and the toxic yellow. Here are some images working well, once the clay body shows through it the overall look is off white but not normally yellow. http://isleofmanpotter.blogspot.com/2012/06/sneak-peek-shh.html?m=1 Link to comment Share on other sites More sharing options...
Guest JBaymore Posted December 18, 2012 Report Share Posted December 18, 2012 Contamination from chrome fumes? but it still happens even when there's not chrome in the kiln. If it happens when ther eis no chrome in the kiln ... then it is not this. Patches of reduction? but it happens to one pot and not it's neighbour some times and in relatively empty kilns some times too. It also happens in different areas of the kiln. Yellow from trace or low levels of iron is typically an indication of oxidation. One good possibility is unevenness of the firing heat work wise. Scatter some cone packs in the kiln around the ware and monitor the relationship between the yellow and what the cones next to the yellow areas are saying. I'm not ruling out thickness of application either but it's not the clay showing through it's a sort of bright toxic yellow fog in the glaze, it's also not as shiny as the white. My first thought was thickness of application with the yellow being thinner. The image you posted and the verbal description you gave do not match....so that confuses the issue. best, ......................john Link to comment Share on other sites More sharing options...
neilestrick Posted December 18, 2012 Report Share Posted December 18, 2012 Ditch the titanium. It's causing the pearl-white, but where it's thinner or breaks it goes yellow. If you just want white, use 10% zircopax/superpax like Brian suggested and get rid of the titanium and tin. Link to comment Share on other sites More sharing options...
Pres Posted December 19, 2012 Report Share Posted December 19, 2012 Ditch the titanium. It's causing the pearl-white, but where it's thinner or breaks it goes yellow. If you just want white, use 10% zircopax/superpax like Brian suggested and get rid of the titanium and tin. Interesting, as I have been firing in ^6 ox. I have been playing around with line blends of mixed opacifiers. I have not found a whole lot out there on mixing them, but I am finding that at least a ^6 there can be some beneficial combinations. When I can confirm, and know more I will post here in a new strand. I am looking at the way they react with underglaze and inglaze combinations Link to comment Share on other sites More sharing options...
pricklypotter Posted December 20, 2012 Report Share Posted December 20, 2012 Seems to me John is right about the thickness. Examining the picture closely, it seems that even in the bright yellow area the glaze is still white where it pooled (eg inside the seashell texture). And it does seem to break yellower on edges even where the rest is white (I also thought the glaze may be pulling iron from the body, but checking out the clay, it seems to be quite white) Link to comment Share on other sites More sharing options...
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